Exhaust-pipe injection system

ABSTRACT

An exhaust-pipe injection system capable of accurately monitoring a lowered injection pressure generated in a fuel line due to exhaust pipe injection and appropriately perform feedback control for the exhaust injection amount. The exhaust-pipe injection system includes: an exhaust pipe injector that injects fuel to an exhaust pipe of an internal combustion engine; a supply pump that sends a fuel to the exhaust pipe injector via a fuel line; a pressure compensating device provided in the vicinity of the exhaust pipe injector of the fuel line; a fuel pressure sensor provided in the fuel line in an upstream side from the pressure compensating device; and an injection control device that adjusts an injection amount of the exhaust pipe injector based on a monitoring value of the fuel pressure sensor.

TECHNICAL FIELD

The present invention relates to an exhaust-pipe injection system foradding unburned fuel to an exhaust gas of an internal combustion engine,and more particularly, to an exhaust-pipe injection system that performsfeedback control for an exhaust injection amount.

BACKGROUND ART

In recent years, in order to purify environmental pollutants containedin an exhaust gas from an engine, an exhaust gas purifier system havinga diesel particulate filter (DPF) unit, a lean NOx trap (LNT) unit, andthe like provided in an exhaust pipe has been developed. In such anexhaust gas purifier system, the unburned fuel is added to the exhaustgas, and the exhaust gas is heated by oxidizing and burning the fuelusing an oxidation catalyst, so that the purifier is regenerated usingthe exhaust gas having a high temperature.

As a means for adding the unburned fuel to the exhaust gas, exhaust pipeinjection attracts interest, in which exhaust gas recirculation (EGR)control can be applied even when a fuel is added, and a fuel consumptionnecessary to increase a temperature is suppressed to a low value withoutgenerating oil dilution in an engine cylinder. The exhaust pipeinjection is a method of adding unburned fuel to the exhaust gas fromthe exhaust pipe injector provided in the exhaust pipe (for example,refer to Patent Documents 1 and 2)

FIG. 4 illustrates a configuration of the exhaust pipe injection systemin the related art.

The exhaust-pipe injection system 41 that performs exhaust pipeinjection includes a supply pump 12 for pressurizing and sending a fuel,a fuel filter 13 for removing impurities mixed in the fuel, acommon-rail injection system 14 that accumulates the pressurized fuel,an in-cylinder injector 15 that injects the fuel accumulated in thecommon-rail injection system 14 into the inside of the engine cylinder,and an exhaust pipe injector 16 that injects the fuel obtained byremoving impurities using the fuel filter 13 into the exhaust pipe.

In the exhaust-pipe injection system 41, the fuel supplied from the fueltank to the supply pump 12 via a supply line 17 is primarily pressurizedand is sent by the supply pump 12, so that the pressurized fuel passesthrough a primary pressurizing line 18 and a fuel filter 13 provided inthe primary pressurizing line 18 and flows to the supply pump 12 again.

The supply pump 12 is driven by a crankshaft of an engine.

The fuel flowing to the supply pump 12 again is secondarily pressurizedand is sent by the supply pump 12. The pressurized fuel passes throughthe secondary pressurizing line 19 and is accumulated in the common-railinjection system 14.

The high-pressure fuel accumulated in the common-rail injection system14 is injected into the inside of the engine cylinder from thein-cylinder injector 15 via a fuel injection line 20 and is consumed foran engine combustion operation. A surplus fuel unconsumed in thein-cylinder injector 15 and a surplus fuel in the common-rail injectionsystem 14 are returned from return lines 21 and 22 and are discharged tothe fuel tank from a discharge line 23 connected to the return lines 21and 22.

A part of the fuel passing through the fuel filter 13 is split to a fuelline 24 connected to a downstream side of the primary pressurizing line18 and is supplied to the exhaust pipe injector 16 via a fuel line 24.In the fuel filter 13, a fuel pressure sensor 25 for monitoring aninjection pressure in exhaust pipe injection is provided in an upstreamside from a filter unit (not illustrated) in the fuel filter 13.

The in-cylinder injector 15, the exhaust pipe injector 16, and the fuelpressure sensor 25 are connected to an electronic control unit (ECU) 26.The ECU 26 controls the in-cylinder injector 15. The ECU 26 includes aninjection control means 27 that adjusts an exhaust injection amount ofthe fuel by controlling an open/close operation of the exhaust pipeinjector 16 based on a monitoring value of the fuel pressure input fromthe fuel pressure sensor 25 and a desired injection amount.

In this exhaust-pipe injection system 41, exhaust pipe injection isperformed by driving the exhaust pipe injector 16 based on a duty ratio.The duty ratio refers to a ratio of an open time (injection time) of theexhaust pipe injector 16 per unit time. The injection amount (exhaustinjection amount) from the exhaust pipe injector 16 is adjusted bycontrolling the duty ratio of the exhaust pipe injector 16.

When the fuel is injected from the exhaust pipe injector 16 to theexhaust pipe, an internal pressure of the fuel line 24 tends totemporarily decrease so as to reduce the exhaust injection amount. Thisis caused by a balance between a fuel supply of the supply pump 12 and afuel reduction caused by the injection. In particular, this tendencybecomes significant when an engine revolution is low, and an in-cylinderinjection amount is large (low revolution and high torque) because thefuel supply amount of the supply pump 12 is small, and the fuelinjection amount of the engine is large. Therefore, it is necessary tomonitor the injection pressure of exhaust pipe injection (fuel pressurein the fuel line 24) and correct a reduction of the injection amountcaused by the lowered pressure by increasing the duty ratio.

Typically, the exhaust injection amount is controlled using a3-dimensional map (typically, called a BP map) in which an injectioncharacteristic of the exhaust pipe injector 16 is expressed using a dutyratio for the injection pressure and the injection amount (that is, theexhaust injection amount is controlled by determining the duty ratio ofthe exhaust pipe injector 16 with reference to the BP map using theinjection pressure and the desired injection amount). It is desirablethat the injection pressure is measured by arranging the fuel pressuresensor in an exhaust injection path as close to the exhaust pipeinjector 16 as possible. This is because a pressure fluctuation in thevicinity of the exhaust pipe injector 16 affects a change of the exhaustinjection amount.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent No. 4417878

Patent Document 2: Japanese Patent No. 4561467

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, in the vicinity of the exhaust pipe injector 16, a pressurepulsation is generated in the fuel line 24 due to the duty operation(that is, open/close operation of the exhaust pipe injector 16) at thetime of injection. Therefore, if pressure feedback control (FB control)is performed to correct the injection amount based on this value, adeviation in a change of the injection amount further increases, so thatthe injection amount is not stabilized.

In order to avoid such a problem, in the exhaust-pipe injection system41 of the related art, the fuel pressure sensor 25 is arranged in anupstream side from the filter unit of the fuel filter 13. In thisconfiguration, due to a buffering effect of the fuel filter 13, it ispossible to reduce influence of the pressure pulsation of the fuel line24 caused by exhaust pipe injection. However, since a fuel pressuremeasurement position is separated from the exhaust pipe injector 16, itis difficult to accurately measure the lowered injection pressure at thetime of injection and appropriately perform pressure FB control for theexhaust injection amount.

In view of the aforementioned problems, the present invention providesan exhaust-pipe injection system capable of appropriately performingfeedback control for an exhaust injection amount by monitoring a loweredinjection pressure generated in a fuel line due to exhaust pipeinjection.

Means for Solving the Problems

In order to achieve the above object, the present invention is anexhaust-pipe injection system including: an exhaust pipe injector thatinjects fuel to an exhaust pipe of an internal combustion engine; asupply pump that sends fuel to the exhaust pipe injector via a fuelline; a pressure compensating means provided in the vicinity of theexhaust pipe injector of the fuel line; a fuel pressure sensor providedin the fuel line in an upstream side from the pressure compensatingmeans; and an injection control means that adjusts an injection amountof the exhaust pipe injector based on a monitoring value of the fuelpressure sensor.

It is preferred that the pressure compensating means suppresses afluctuation in the monitoring value of the fuel pressure sensor causedby an open/close operation of the exhaust pipe injector.

It is preferred that the injection control means adjusts the injectionamount of the exhaust pipe injector by controlling an open time of theexhaust pipe injector.

It is preferred that the injection control means adjusts the injectionamount of the exhaust pipe injector based on the monitoring value of thefuel pressure sensor to correct a reduction of the injection amountcaused by a lowered fuel pressure of the fuel line.

It is preferred that the pressure compensating means includes a buffertank.

It is preferred that the pressure compensating means includes anaccumulator.

Effects of the Invention

According to the present invention, it is possible to provide anexhaust-pipe injection system capable of appropriately performingfeedback control for an exhaust injection amount by accuratelymonitoring a lowered injection pressure generated in a fuel line due toexhaust pipe injection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a configuration of anexhaust-pipe injection system according to an embodiment of the presentinvention.

FIGS. 2A and 2B are diagrams illustrating a fluctuation in the fuelpressure when the exhaust pipe injector is opened or closed, in whichFIG. 2A illustrates a fluctuation in the fuel pressure of theexhaust-pipe injection system according to the present invention, andFIG. 2B illustrates a fluctuation in the fuel pressure of anexhaust-pipe injection system obtained by arranging a fuel pressuresensor in the vicinity of the exhaust pipe injector without providing apressure compensating means.

FIG. 3A is a partially cross-sectional view illustrating a configurationof the exhaust-pipe injection system according to another embodiment ofthe present invention, and FIG. 3B is a diagram illustrating acharacteristic of an accumulator.

FIG. 4 is a schematic diagram illustrating a configuration of an exhaustinjection system in the related art.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, exemplary embodiments of the present invention will bedescribed with reference to the accompanying drawings.

FIG. 1 is a schematic diagram illustrating a configuration of anexhaust-pipe injection system according to an exemplary embodiment ofthe present invention.

The exhaust-pipe injection system 11 according to the present embodimenthas basically the same basic structure as that of the exhaust-pipeinjection system 41 of the related art. Therefore, like referencenumerals denote like elements, and description thereof will not berepeated.

In the exhaust-pipe injection system 11, a pressure compensating means28 is provided in the vicinity of the exhaust pipe injector 16 of thefuel line 24, and a fuel pressure sensor 29 is provided in the fuel line24 in the upstream side from the pressure compensating means 28. Thepressure compensating means 28 is provided to suppress a pulsation inthe fuel line 24 caused by the open/close operation (duty operation) ofthe exhaust pipe injector 16 and a fluctuation in the monitoring valueof the fuel pressure sensor 29. According to the present embodiment, thepressure compensating means 28 includes a buffer tank. The buffer tankhas a minimum necessary capacity (for example, approximately 200±100 cc)such that a pulsation component in the fuel line 24 can be absorbed, andan average value of the pressure reduction amount at the time ofinjection is not changed.

The ECU 26 is connected to the in-cylinder injector 15, the exhaust pipeinjector 16, and the fuel pressure sensor 29. In addition, an injectioncontrol means 27 integrated into the ECU 26 adjusts an injection amountof the exhaust pipe injector 16 by controlling an open time of theexhaust pipe injector 16 based on the monitoring value of the fuelpressure sensor 29.

More specifically, the injection control means 27 determines a dutyratio of the exhaust pipe injector 16 with reference to a BP map using amonitoring value of the fuel pressure sensor 29 and a desired injectionamount output by the ECU 26 and adjusts the injection amount of theexhaust pipe injector 16 by controlling the open time of the exhaustpipe injection injector 16 based on the determined duty ratio. Inaddition, the injection control means 27 performs pressure feedback (FB)control for the injection amount based on the monitoring value of thefuel pressure sensor 29 such that, when the fuel pressure (injectionpressure) in the fuel line 24 is lowered due to injection of the exhaustpipe injector 16, a reduction of the injection amount caused by thelowered fuel pressure is corrected by changing the duty ratio andcontrolling the open time of the exhaust pipe injector 16 with referenceto the BP map using the monitoring value of the lowered fuel pressureand the desired injection amount.

Next, effects of the present invention will be described with referenceto FIG. 2.

FIGS. 2A and 2B are diagrams illustrating a fluctuation in the fuelpressure of the open/close operation of the exhaust pipe injector 16, inwhich FIG. 2A illustrates a fluctuation in the fuel pressure of theexhaust-pipe injection system 11 according to the present invention, andFIG. 2B illustrates a fluctuation in the fuel pressure of theexhaust-pipe injection system having the fuel pressure sensor 29 in thevicinity of the exhaust pipe injector 16 without providing the pressurecompensating means 28. Here, a change of the monitoring value (fuelpressure) of the fuel pressure sensor 29 during the exhaust pipeinjection is illustrated while the exhaust pipe injector 16 isopened/closed (in a period indicated by a dotted line in the drawing) bysetting the duty ratio of the exhaust pipe injector 16 to 80%.

As illustrated in FIGS. 2A and 2B, when the exhaust pipe injector 16 isclosed without performing exhaust pipe injection, a pulsation componentcaused by the supply pump 12 is detected by the fuel pressure sensor 29regardless of whether or not the pressure compensating means 28 isprovided.

When exhaust pipe injection starts, and the exhaust pipe injector 16 isopened/closed, in the exhaust-pipe injection system having the fuelpressure sensor 29 arranged in the vicinity of the exhaust pipe injector16 without providing the pressure compensating means 28, the monitoringvalue of the fuel pressure sensor 29 is influenced by a pressurepulsation in the fuel line 24 caused by the open/close operation of theexhaust pipe injector 16. Therefore, pressure FB control is notappropriately performed, a fluctuation of the fuel pressure during theexhaust pipe injection increases as illustrated in FIG. 2B, and adeviation in a change of the injection amount increases, so that it isdifficult to stabilize the injection amount.

Meanwhile, in the exhaust-pipe injection system 11 according to thepresent embodiment, using the pressure compensating means 28 (buffertank), it is possible to suppress the pressure pulsation caused by theopen/close operation of the exhaust pipe injector 16 from influencing afluctuation of the monitoring value of the fuel pressure sensor 29.Therefore, it is possible to appropriately perform pressure FB control,suppress the fuel pressure during the exhaust pipe injection asillustrated in FIG. 2A, and stabilize the injection amount.

The average fuel pressure monitored by the fuel pressure sensor 29during exhaust pipe injection is represented in Table 1.

TABLE 1 Average fuel pressure [kPa] Buffer tank Provided 768.4 Notprovided 767.1

As recognized from Table 1, the average fuel pressure during exhaustpipe injection in the exhaust-pipe injection system 11 having thepressure compensating means 28 (buffer tank) is approximately equal tothat of the exhaust-pipe injection system having no pressurecompensating means 28. That is, it is conceived that the exhaust-pipeinjection system 11 can perform pressure FB control for the injectionamount by suppressing only the pulsation component of the fuel line 24and stabilize the injection amount.

In summary, in the exhaust-pipe injection system 11 having a simple andinexpensive configuration according to the present embodiment, it ispossible to suppress a pressure fluctuation in the fuel line 24 causedby the open/close operation of the exhaust pipe injector 16 using thepressure compensating means 28 and accurately monitor the fuel pressureof the fuel line 24 using the fuel pressure sensor 29 provided in thevicinity of the exhaust pipe injector 16 while a pressure fluctuation issuppressed.

In addition, when the fuel pressure (injection pressure) in the fuelline 24 is lowered due to injection from the exhaust pipe injector 16,it is possible to accurately monitor the lowered injection pressure,appropriately perform pressure FB control for the exhaust injectionamount, and correct a reduction of the injection amount caused by thelowered injection pressure.

As a result, it is possible to improve a temperature stability toregenerate a DPF unit or an LNT unit or a stability of a λ-value(exhaust gas air-fuel ratio) at the time of desulfurization control bycontrolling a temperature of the exhaust gas.

In addition, it is possible to handle a driving condition change of aninternal combustion engine or a change of the injection pressure causedby degradation of the exhaust pipe injector 16.

The present invention is not limited to the aforementioned embodiment.For example, an accumulator may be provided as the pressure compensatingmeans 28 instead of the buffer tank.

FIG. 3A is a partially cross-sectional view illustrating an exhaust-pipeinjection system 31 having an accumulator 32 provided in the vicinity ofthe exhaust pipe injector 16 of the fuel line 24 as the pressurecompensating means 28.

The accumulator 32 has a maximum absorption capability for a pulsationwhen the frequency thereof is equal to the pulsation frequency (resonantfrequency) of the fuel line 24 as illustrated in FIG. 3B. For thisreason, the pulsation frequency of the fuel line 24 is previouslymeasured, and the accumulator 32 is designed based on the followingEquation (1) such that the pulsation frequency is equal to the frequencyf of the accumulator 32.

$\begin{matrix}{f = {\frac{1}{20\; \pi}\sqrt{\frac{n \cdot P \cdot A}{10\; {\rho \cdot l \cdot {Vg}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

where n denotes a polytropic index (n=1.4),

p denotes a pressure of the port entrance [MPa],

A denotes a cross-sectional area of the port [mm²],

ρ denotes an oil density [N/mm⁴-s^(2] (ρ=)8.7×10¹⁰),

l denotes a length of the port [mm], and

Vg denotes a gas volume of the accumulator in operation [cm³].

In this manner, in the exhaust-pipe injection system 31 according to thepresent embodiment, it is possible to obtain excellent effects similarto those of the exhaust-pipe injection system 11 described above.

EXPLANATION OF REFERENCE NUMERALS

11 exhaust-pipe injection system

12 supply pump

16 exhaust pipe injector

24 fuel line

27 injection control means

28 pressure compensating means (buffer tank)

29 fuel pressure sensor

1-6. (canceled)
 7. An exhaust-pipe injection system comprising: anexhaust pipe injector that injects fuel to an exhaust pipe of aninternal combustion engine; a supply pump that sends fuel to the exhaustpipe injector via a fuel line; a pressure compensating means provided inthe vicinity of the exhaust pipe injector of the fuel line; a fuelpressure sensor provided in the fuel line in an upstream side from thepressure compensating means; and an injection control means that adjustsan injection amount of the exhaust pipe injector based on a monitoringvalue of the fuel pressure sensor.
 8. The exhaust-pipe injection systemaccording to claim 7, wherein the pressure compensating means suppressesa fluctuation in the monitoring value of the fuel pressure sensor causedby an open/close operation of the exhaust pipe injector.
 9. Theexhaust-pipe injection system according to claim 7, wherein theinjection control means adjusts the injection amount of the exhaust pipeinjector by controlling an open time of the exhaust pipe injector. 10.The exhaust-pipe injection system according to claim 7, wherein theinjection control means adjusts the injection amount of the exhaust pipeinjector based on the monitoring value of the fuel pressure sensor tocorrect a reduction of the injection amount caused by a lowered fuelpressure of the fuel line.
 11. The exhaust-pipe injection systemaccording to claim 9, wherein the injection control means adjusts theinjection amount of the exhaust pipe injector based on the monitoringvalue of the fuel pressure sensor to correct a reduction of theinjection amount caused by a lowered fuel pressure of the fuel line. 12.The exhaust-pipe injection system according to claim 7, wherein thepressure compensating means includes a buffer tank.
 13. The exhaust-pipeinjection system according to claim 7, wherein the pressure compensatingmeans includes an accumulator.